YY/T 1552-2017Implants for surgery-Measurements of open-circuit potential to assess corrosion behaviour of metallic implantable materials and medical devices over extended time periods (English PDF)

3.1 Corrosion potential

The electrode potential of the metal in a particular corrosion system.

3.2 Corrosion system

The system consists of one or more metals and environmental parts that affect corrosion, including samples, electrolytes, and electrodes.

3.3 Environmental test conditions

Test conditions for samples (samples), including temperature, gas environment, pH, label, volume, and liquid exchange rate.

3.4 Self-corrosion potential

The corrosion potential when there is no net (external) current flowing in or out of the metal surface.

3.5 Isotonic sodium chloride (NaCl) solution isotonic NaClsolution

An aqueous solution of sodium chloride (0.9% by mass) which has the same surface tension as living tissue.

Note. Application in surgery can prevent tissue damage.

3.6 Open circuit potential

The electrode potential measured relative to the reference electrode or other electrode when no current flows in or out. See self-corrosion potential (3.4).

3.7 Passivation film

Note. Passivation films are usually attached to metal surfaces and have submicroscopic thickness (see ISO 8044).

3.8 Reference electrode

Electrodes with stable and reproducible potentials are used as reference in electrode potential measurements.

3.9 Working electrode

The test or working electrode in the electrolytic cell, that is, the test sample mentioned in the text of this standard.

4.1 Principles

In this electrochemical test method, the sample (sample) is immersed in isotonic chlorine associated with the physiological environment of the human body as described in ISO 16428.

Sodium test solution. Other test solutions and environmental conditions are also described in ISO 16428. Low pH acidic solution as more stringent See Appendix A for the harsh test conditions.

The test was carried out in an electrolytic cell similar to that described in ASTM G5. Electrodes and other necessary equipment can be placed in the electrolytic cell (see picture 1). Description. 1---working electrode (sample); 2---intake; 3---exhaust; 4---drainage; 5---test solution (electrolyte); 6---into the water; 7---Lujin capillary; 8---reference electrode; 9---thermometer.

Figure 1 Example of electrolytic cell When the sample is exposed to the environment for a specific period of time, the continuous recording of the open circuit potential changes with time begins. Sample as work The electrode was measured for its electrochemical behavior relative to the reference electrode (see Figure 2). Description. 1---working electrode (sample); 2---potential measuring instrument (potentiometer); 3---reference electrode.

Figure 2 Example of circuit for measuring open circuit potential

4.2 Significance of the measurement method

The open circuit potential reflects the (electrochemical) reaction that occurs on the surface of the sample (working electrode) that is in contact with the test solution. According to the conditions Similarly, usually after the sample is immersed for 1h or 2h, the reaction of the surface (electrode) of the sample in contact with the test solution (electrolyte) reaches equilibrium, and the potential Become more stable. At the beginning of the test, the potential value of the passivation material increases, usually to a (more) positive direction, indicating that the sample is passivated in the solution.

Or as the corrosion resistance increases, its passivation is enhanced. A decrease in potential indicates that the surface is activated as the passivation characteristics decrease or disappear.

Thereby exhibiting the sensitivity of corrosion. The potential value at steady state, the change in potential value, the stability and instability of the potential can be reflected in the passivation film The electrochemical process on the corrosion behavior of the material being studied.

Note. Chloride ions in the isotonic sodium chloride test environment are corrosive. The enhanced passivation in the solution indicates the initial corrosion resistance of the corresponding material. Higher.

This test method is very sensitive and requires careful handling and control of each step, especially the surface of the sample, while understanding the entire process.

The state is critical and the pre-processing process needs to be done carefully and guaranteed to be reproducible.

4.3 Application

The electrochemical test method is suitable for studying the long-term passivation and corrosion behavior of materials and surgical implanted instruments and their metallurgical properties and processes. And the relationship between surface conditions.

When such an open circuit potential measurement method is combined with a mechanical test, information on the mechanical stability of the passivation film can also be provided.

This test method can be used to screen materials, compare materials and surface treatment processes, optimize corrosion resistance, and study and characterize material systems. for Extending the evaluation range, this test method can be used in conjunction with other electrochemical corrosion experiments.

Note. Terms such as corrosion system (3.2) or corrosion potential (3.1) do not imply that significant corrosion will occur. In other words, these terms are derived from the corrosion mechanism and A scientific definition of the perspective of its evaluation.

5.1 Electrolysis cell

The electrolytic cell consists of a suitable glass container, in principle similar to that given in ASTM G5. Figure 1 shows the display of the electrolytic cell Example (flat bottom type). If the system is not expected to be used for constant/dynamic potential measurements, the counter electrode (auxiliary electrode) may not be used.

Note. Borosilicate glass has proven to be suitable for use as a glass container (ISO 3585). If the open circuit potential measurement is combined with mechanical experiments or for other reasons, the electrolytic cell The container can be designed separately and is glass-free (ISO 16428).

5.1.1 Working electrode

The working electrode is a sample.

5.1.2 Reference electrode

Saturated calomel electrodes (SCE) or other electrodes can be used. However, in order to facilitate the comparison of the data, the latter should also be converted into Relative to the value of SCE.

5.1.3 Lu Jin Capillary in Salt Bridge

Connected to the reference electrode. The distance between the capillary tip and the surface of the sample should be 2 mm or equal to the diameter of the tip of the capillary. Its larger value.

5.1.5 Thermometer

Used to measure the temperature of the test solution.

This device is suitable for long-term recording of data with an impedance of >1011ohm and a sensitivity of 1mV for monitoring potential changes. Measurement range from -1V~ 1.5V, if the test system requires it, you can choose a larger measurement range.

5.3 pH meter

The sensitivity is ±0.1.

5.4 Constant temperature system

The temperature of the test solution was maintained at (37 ± 1) °C in a suitable manner (water bath, heating tube, etc.).

Note. In tests using a potentiodynamic measurement system, a platinum electrode is suitable as a counter electrode (auxiliary electrode).

6.1 Sample type

In comparable systems studied, material samples should be of similar form and size (eg rods, tubes, plates, sheets). When implantable devices When tested, it can be tested in its original form. If the device needs to be divided into several parts, the separate surface and the original surface are different This difference may affect the measurement, which needs to be taken into account. Applying an inert, adhesive non-conductive material to separate surfaces Electrical materials may be a useful method, however, it is necessary to ensure that this does not cause localized corrosion, such as pitting or crevice corrosion.

6.2 Surface preparation

The preparation of the sample surface is a key part of this test and the repeatability of this process is an important requirement. Open circuit potential research institute The required surface preparation depends on the research purpose, depending on the specific surface treatment process (physical, mechanical, heat treatment, etc.) and grinding/polishing/cleaning/can The time between the possible drying/probable sterilization/storage and the preparation of the sample to the measurement is specified. The sample should be free before immersing in the solution Grease and other secondary pollution. This needs to be cleaned with pure ethanol and rinsed with pure water in accordance with ISO 3696.

If the passivation behavior of the material needs to be measured without being affected by a certain surface treatment process (such as electrolytic polishing, sterilization, etc.)

The amount should be prepared in time before the start of the test. It can be wet-ground with SiC sandpaper No. 240 and No. 600, then rinsed with water.

The grease is removed from pure ethanol and finally rinsed with pure water in accordance with ISO 3696. The steps of surface preparation should be recorded.

6.3 Assembly of the sample

In general, the assembly of the sample should ensure reliable connection of the circuit outside the electrolyte, and the assembly of the sample will not bring measurement error and local corrosion. Corrosion such as pitting or crevice corrosion.

The specimen can be assembled to the connecting rod by means of a thread, and the connecting rod is also treated by a surface method similar to the specimen, or the specimen itself is only Partially immersed in the solution to establish a reliable circuit connection on the portion of the sample outside the solution. In the comparative study, the portion of the sample immersed in the solution should be the same.

7.1 General

Environmental conditions should generally follow ISO 16428.

7.2 Test solution

An isotonic sodium chloride solution conforming to ISO 16428 was used as the test solution.

Phosphate buffered sodium chloride solutions can also be used when using the necessary technical protective measures (see ISO 16428 and YY/T 0695).

If more stringent conditions are required to study corrosion behavior, analytically pure hydrochloric acid can be added to achieve the defined pH requirements.

Acidic sodium chloride solution (see Appendix A). Alternatively, a multiple increment of 0.9% sodium chloride solution can be used (see A.3).

There are some reasons for using other forms of test solutions. These solutions and other isotonic solutions other than 0.9% sodium chloride The liquid should be reflected in the report. Other solution forms are included in ISO 16428 and YY/T 0695.

7.3 Temperature

During the test, the temperature should be kept at (37 ± 1) °C.

7.4 pH

The pH before, after, and during the test should be recorded at a frequency appropriate for the system under test.

7.5 Ventilation

Gas should be continuously introduced into the solution during the test. Beware of air bubbles on the surface of the sample and interference with the measurement.

The test results will be affected by the presence of oxygen in the solution. The solution is purified by.

a) use pure oxygen to facilitate passivation;

b) Simulate the evacuation of oxygen using pure nitrogen (no oxygen); in this case, pass nitrogen for 0.5 h before the start of the test.

For ease of comparison, the test can be carried out in gas and/or air.

Blowing nitrogen purification requires the use of a sealed electrolytic cell. Under nitrogen purge conditions, it may take more than 30 minutes to stabilize the system. Set the state.

7.6 Test solution volume

For the comparability of the test, the volume of the test solution should be the same. Generally, the electrolytic cell should be filled with 500mL~1000mL. liquid. The ratio of the volume of the test solution to the surface area of the sample should be at least 10 mL/cm2.

8.1 Establishment of the test

The electrolyte was injected into the electrolytic cell and a salt bridge containing the test solution was placed. When the temperature of the solution is stable, the selected gas is passed. then The pH was measured. Assemble the sample, immerse the sample in the test solution, and connect the circuit. Adjust the tip of the salt bridge to the surface of the sample, and Adjust the distance to approximately 2mm. Then start recording the open circuit potential.

8.2 Test cycle

The experiment was carried out as long as necessary to obtain the electrode potential stability value of the test system under certain conditions. As the first For the secondary screening, the open circuit potential should be recorded for 3 days.

If the open circuit potential measurement is combined with a mechanical test, the latter should be determined during the recording process.

8.3 Observation results

Pay attention to any abnormalities during the test and discoloration and decomposition of the test solution.

At the end of the test, the samples were examined under a low power microscope for any corrosive surface changes and localized corrosion.

Interpret the test results based on relevant experience and expertise of electrochemistry.

A.1 General

As a harsh test condition, the open circuit potential can be measured in a solution containing an increase in the concentration of chloride ions to investigate the stability of the potential.

Qualitative and passivating conditions. Solutions with higher chloride ion concentrations can be prepared according to A.2 or A.3.

For the control test, one of the tests can use a stepwise increase in the chloride ion concentration to obtain the test solution.

A.2 Low pH sodium chloride solution

The pH of the isotonic sodium chloride 0.9% (mass fraction) solution is 6.8 to 7.4. Adding analytically pure hydrochloric acid to such a solution Prepare the solution to obtain the following pH values.

a) pH6;

b) pH5;

c) pH4;

d) pH3; e) pH2.

A.3 Solution to increase the concentration of sodium chloride

A 0.9% analytical pure sodium chloride solution using a pure water preparation in accordance with ISO 3696.

a) 1.8% sodium chloride;

b) 2.7% sodium chloride;

c) 3.6% sodium chloride;

d) 4.5% sodium chloride. references [1] YY/T 0695-2008 Standard Test Method for Cyclic Potent Potential Polarization of Corrosion Sensitivity of Small Implant Devices [2] ISO 11845.:1995 Corrosionofmetalsandaloys-Generalprinciplesforcorrosiontesting [3] ISO 3585Borosilicateglass3.3-Properties [4] ISO 8044Corrosionofmetalsandaloys-Basictermsanddefinitions [5] ASTM G3StandardPracticeforConventionsApplicabletoElectrochemicalMeasurements inCorrosionTesting [6] ASTM G5StandardReferenceTestMethodforMakingPotentiostaticandPotentiodynamic AnodicPolarizationMeasurements [7] ASTM G15StandardTerminologyRelatingtoCorrosionandCorrosionTesting [8] JIS T0302Testingmethodforcorrosionresistanceofmetalicbiomaterialsbyanodicpolari- Zationmeasurement [9] Pharmacopoeia of the People's Republic of China (2015 Edition)